Susceptibility breakpoint for cefquinome against Escherichia coli and Staphylococcus aureus from pigs

Cefquinome is the only fourth-generation cephalosporin used solely for veterinary applications.In this study,we established the wild-type cut-off(CO_(WT))and pharmacokinetic/pharmacodynamic cut-off(CO_(PD))of cefquinome against Escherichia coli and Staphylococcus aureus.A total of 210 E.coli and 160 S.aureus isolates were collected from pigs in Guangdong Province between 2014 and 2018.The minimum inhibitory concentrations(MICs)were determined using a microdilution broth method.MIC_(50)and MIC_(90)were 0.06 and 0.25μg m L^(–1)for E.coli and 0.5 and 1μg m L^(–1)for S.aureus,respectively.Statistical analysis and the ECOFFinder Program showed that the CO_(WT)for cefquinome against E.coli and S.aureus were0.125 and 2μg m L^(–1),respectively.The resistance rates were 11.9%for E.coli and 6.25%for S.aureus.Based on a5000-subject Monte Carlo simulation,the CO_(PD)value for cefquinome against E.coil and S.aureus was 0.25μg m L^(–1)under the recommended dose(2 mg kg^(–1),twice a day for 3 days),confirming that infections caused by strains with MIC≤0.25μg m L^(–1)could be effectively treated.Following adjustment of the dosing regimen to 4.5 mg kg^(–1),effective treatment(>90)was achieved for S.aureus infections with MIC_(90)1μg m L^(–1).This susceptibility breakpoint determination is significant for resistant surveillance and cefquinome dosage guidance against E.coli and S.aureus in pigs.